Characteristics of backward-inclined non-premixed jet flames in crossflow

Abstract

The characteristics of backward-inclined non-premixed jet flames in a uniform crossflow were studied in a wind tunnel. Time-averaged photography techniques were used to study flame behavior. The flow field was captured by short exposure photography and Mie-scattering techniques. Flame temperatures were probed with a fine-wire R-type thermocouple. In the domain of jet-to-crossflow momentum flux ratio R and backward-inclination angle θ, the flames were categorized into three characteristic modes. The first mode consisted of crossflow dominated flames characterized by a down-wash recirculation flame in the wake of the burner tube. The second mode consisted of transitional flames characterized by a yellowish recirculation flame and a tail flame. The third mode consisted of jet dominated flames characterized by a blue flame base and an absence of the down-wash flame. The down-wash recirculation flames were observed for a backward inclination angle of θ < 40°. The ability of the flames to resist blow off when increasing the jet-to-crossflow momentum flux ratio decreased as θ increased. Coherent vortices were observed on the seeded fuel jet, whose type was dependent on R and θ. In the upstream region, the fuel appeared above the flame. However, in the downstream region, the fuel became engulfed within the flame. For a fixed θ, the Strouhal number of the upwind shear layer vortices on the fuel jet was observed to decrease asymptotically as R increased. In the near-field at x/d ≈ 5, the crossflow dominated flames presented temperature profiles characterized by a broad dual-hump peak profile in the symmetry plane, while in the near-field at x/d ≈ 5, the jet dominated flames presented a single peak profile in the symmetry plane.